Composite stator concentric linear induction motor

ABSTRACT

A linear induction motor having an elongated secondary or rotor member, and a cylindrical hollow primary or stator member having teeth formed as washers with energizable coils between the washers. The stator and coils concentrically surround the rotor member. The stator teeth have an inner washer or facing of a material having higher magnetic permeability and saturation properties than the stator to thereby provide composite stator teeth which do not magnetically saturate when high rotor forces are required for small diameter rotors. The motor has a particular utility in removing a workpiece from a die or other forming means.

1 198502 OR BAH Z0627 United States Patent 1191 I 1111 3,852,627

Davis 1451 Dec. 3, 1974 1 COMPOSITE STATOR CONCENTRIC LINEAR INDUCTION MOTOR Primary Examiner-Donovan F. Duggan [76] lnvei'mor: Murray w. Davis, 20501 Attorney, Agent, or F1rmCullen, Settle, Sloman &.

Woodmont, Harper Woods, Mi Cantor 48225 [22] Filed: Apr. 9, 1973 7] ABSTRACT [211 App]' 349227 A linear induction motor having an elongated secondary or rotor member, and a cylindrical hollow pri- [52] U.S. Cl 310/13, 310/42, 310/216, mary or stator member having teeth formed as wash- 310/218 ers with energizable coils between the washers. The [51 Int. Cl. H02k 41/02 stator and coils concentrically surround the rotor [58] Field 01' Search 310/13, l2, 14, 45, 92, member. The stator teeth have an inner washer or fac- 310/216-218, 190-193, 49 ing of a material having higher magnetic permeability and saturation properties than the stator to thereby [56] References Cited provide composite stator teeth which do not magneti- UNITED STATES PATENTS cally saturate when high rotor forces are required for 2 453 539 11/1948 ,Reardon 310/42 X a small diameter rotors. The motor has a particular util- 2 519 27? 8/1950 Nesbitt ei';ilill""'"1111111310/45 ux ity in removing a workpiece from a die or other form 3,602,745 8/1971 Davis 310/13 means- 3,668,444 6/1972 Davey 310/13 X 13 C D FOREIGN PATENTS OR APPLICATIONS 8 F'gures 906.712 9/1962 Great Britain 310/12 through the stator.

COMPOSITE STATOR CONCENTRIC LINEAR INDUCTION MOTOR BACKGROUND OF THE INVENTION The invention herein relates to a linear induction motor which is an improvement over that disclosed in my US. Pat. No. 3,602,745, issued Aug. 31, 1971.

Many applications for tubular or concentric linear induction motors require a high force on a rotor of a small diameter or cross-sectional area. These rotors may consist of small solid wires or rods of electrically conductive material or hollow tubes of electrically conductive material which may also contain rotor core material. Whether they be hollow or solid, the basic characteristic is a small cross-sectional area.

Problems arise in the design of linear induction machines which require large electromagnetic forces on the rotors having small cross-sectional areas. This necessitates the use of a very long stator member which has its own resultant design problems. For example, a prior art linear induction motor such as that disclosed in my US. Pat. No. 3,602,745, if utilized with a rotor of a small cross-sectional area, would have to be very long to provide a high rotor force, since the force generated depends largely on the total surface area of the rotor.

Another problem is magnetic saturation of the iron in the stator and in the rotor core if the rotor core should contain iron. Magnetic saturation may result when high magnetic flux densities are necessary to produce the required force necessary to pull the roto Thus, the invention herein relates to an improved linear induction motor which can create high rotor forces SUMMARY OF THE INVENTION The invention herein contemplates an improved linear induction motor having an elongated secondary or rotor member and cylindrical hollow primary or stator member having teeth formed as washers with slots therebetween to receive energizable coils. The stator andcoils concentrically surround the rotor member. The stator teeth have a facing or an insert of a material having higher magnetic permeability and saturation properties than the statormember to thereby provide a composite stator tooth which does not magnetically saturate when rotors having small cross+sectional areas are utilized, while still providing high rotor forces.

The present invention has uses whether the rotor is hollow in cross-section, such as a tube, or solid such as a wire or rod. For example, the use of a composite stator tooth provides the force necessary to extrude a wire, rod or tube from an extrusion die. Furthermore, the force generated by the improved linear induction motor may be utilized to form or draw a hollow tube about a mandrel.

Various forms of facings and inserts on the stator teeth are disclosed and the particular shape of the facing may be designed based upon'the maximum magnetic flux density necessary in a particular application.

Means are also provided for air cooling the linear induction motor such as by providing apertures in the stator members and a manifold connected thereto through which air may be circulated through the motor.

DESCRIPTION OF THE DRAWINGS The improved linear induction motor, together with its various advantages, will become apparent upon reading the following detailed description taken in conjunction with the following drawings.

In the drawings, wherein like reference numerals identify corresponding parts:

FIG. I is a fragmentary perspective illustration of a concentric linear induction motor having a composite stator tooth;

FIG. 2 is a partial assembly drawing of the motor of FIG. 1;

FIG. 3 is a cross-sectional view of a linear induction motor as described herein;

FIG. 4 is a perspective illustration of an individual stator tooth of the motor of FIGS. 1-3 with the facinging yet another structure for the facing on a stator tooth.

DETAILED DESCRIPTION .With reference to the drawings, the linear induction motor 10 includes a hollow, cylindrical stator I2 which may be a composite assembly of alternatingstator rings 13 and stator washers or teeth 14. Upon assembly of the stator, there is an annular slot or opening 16 between adjacent teeth to receive electrically energizable coils 17 which may be wound on spools 18. v

The coils l7 and stator washers and rings together make up a rigid stator 12 which may be fixed against movement by securing the same within a suitable housing or which is rigid in and of itself if bolts 19 are passed through suitable apertures in the stator washers and stator rings as illustrated in FIG. 2.

Arranged concentrically within the stator and its coils are rotor means as illustrated in FIGS which may include either a rotor core 20, a rotor tube 22 or both the rotor core and the tube as set forth in my US. Pat.

No. 3,602,745. The rotor means has been omitted from FIGS. 1 and 2 for greater clarity.

The particular structure of the rotor means varies depending upon the application or use of the motor..

Thus, the motor of the present invention may be utilized with or without a rotor core 20 to extrude a thin, hollow tube 22 from an extrusion die.

FIG. 4 illustrates, in perspective, an individual stator tooth or washer 24. The problem of magnetic saturation may be explained by considering a sector 26 on the outer periphery of the stator tooth 24 which receives a particular amount of flux. The flux moves radially inward, within a tooth, from the outer area 26 down through the tooth to the inner area 28 on the face of the tooth.

Since the flux is constant and since the surface area at the periphery or outer portion of the tooth 26 is greater than the inner portion 28, it is immediately apparent that the flux density or flux per unit area increases toward the inner portion of the stator tooth.

However, the size of the inner tooth face as at 28 is related to the circumference and thus to the crosssectional area of the rotor means. Thus, as the rotor has an increasingly smaller diameter, the inner flux ring of the individual stator tooth gets smaller, thus increasing flux density and tending to push the stator higher into saturation.

To overcome this problem, the invention contemplates the use of a composite stator member having, at its inner regions, a material having a magnetic permeability and saturation level higher than those of iron.

For example, vanadium permendur is an alloy of iron and cobalt having approximately 49 percent of each with about 2 percent vanadium. This material has a very high magnetic saturation level, it is exceptionally highly permeable, and provides for low core losses. Unfortunately, this material is prohibitively expensive and cannot be utilized economically for the stator of a linear induction motor.

I have discovered that it is possible to utilize this type of material only as a facing on the inner area of the stator teeth. The thickness and shape of the facing may be mathematically determined, based upon the flux densities necessary in a particular application.

For example, with reference to FIGS. and 6, there is illustrated the use of a facing or insert of vanadium permendur in the form of a washer. This washer has a thickness or axial dimension 31 substantially the same as the axial thickness of an individual tooth 24.

In the forming of the composite stator tooth structure, it is noted that the portion of the stator tooth which will be of iron is shorter, as at L in FIG. 5 than the corresponding length M of a tooth 14 illustrated in FIG. 3. The precise length of the facing may be calculated based upon the flux densities to be utilized in order to prevent the iron from becoming magnetically saturated.

With reference to FIG. 7, there is illustrated a nonuniform thickness composite stator tooth which may be employed to increase the total flux through the stator teeth. The stator tooth of FIG. 7 includes a composite tooth having electrical grade iron as at 32 and a facing of a material of a higher magnetic permeability such as vanadium permendur as at 34. It is noted that the facing material 34 is axially of a greater dimension than the axial'dirnension of an individual iron stator tooth 32.

FIG. 7 illustrates flux lines 36 showing the divergence of the magnetic flux through the facing 34. Since vanadium permendur is expensive and, since portions of the facing 34 do not receive the diverging flux lines 36, these portions may be removed.

Specifically, FIG. 8 illustrates another embodiment of the shape of the facing which takes the form of an inverted T, as at 38. This provides an optimum shape for the vanadium permendur facing. An encapsulating material 39 may be used between adjacent facings for insulation and rigidity. It must be appreciated that all g the shapes of the facings disclosed will permit highly set forth in my prior US. Pat. No. 3,602,745 if there is sufficient room for them.

, .lustrates the stator having collars 40 through which the 65 I rotor means maypass. Bearings 42 may be utilized as To overcome the problem of heat a plurality of slots 44 are provided in the stator rings 13 and a manifold 46 is connected from a source of air 48 to these slots. Above each coil 17 is a rectangular, annular channel 50 between the sides of the spool 18. Each is in communication with its slot 44 to define fluid paths through the motor. Air may then be circulated through the slots and channels and thus cool the motor during operation.

In addition to utilizing the motor 10 to extrude hollow tubes 22, or solid wires and rods through a die or other forming means 45, the motor of the present invention may be used to draw a tube 22 around a mandrel or bulb 47. The rotor core 20 itself could serve as the mandrel as indicated by the dotted extension of the core 20 into the forming means. Also, liquid or molten metal may be moved through a stationary hollow tube. Multiple motors, in tandem, may of course be utilized in any of these applications.

The benefit of using the rotor core 20 is that it concentrates the flux density. However, it must be appreciated that since the diameter of the rotor core is smaller than the diameter of the teeth facing the core, the flux density will increase tending to push the core closer towards saturation. Therefore, if a core is used, it must be of a material having a higher magnetic permeability than the iron found in the stator teeth. Vanadium permendur may be utilized for the rotor core.

If the rotor core is'solid, it may be manufactured of vanadium permendur or, it may be a tube of iron having a solid central core of vanadium permendur inserted therein. If a hollow rotor core is used, it may be a tube of vanadium permendur or a tube of iron having an inner facing of vanadium permendur just as the stator has an inner facing 30 of vanadium permendur.

The foregoing is a description of the present invention and should not be taken in a restrictive sense but only as describing the underlying theory of operation. The inventive concepts may be further developed within the scope of the following claims.

I claim:

l. A converging flux, concentric linear induction motor especially adapted for moving rotor means, over long distances, said rotor means having a generally'circular cross-section and a length greatly exceeding its diameter, said motor comprising: I

a hollow, cylindrical stator member made of a material of high magnetic permeability and positioned to surround said rotor means concentrically;

said stator member including a plurality of annular teeth having teeth faces, said teeth being longitudinally spaced apart to define annular slots therebewhereby upon energization of said coils, said small diameter rotor means is 'moved axially by the generation of increased rotor forces without magnetic saturation of the stator member or said discrete facing or rotor means.

2. The motor of claim 1 wherein said discrete facing comprises a hollow washer on each of said teeth, said washer being of the same axial dimension as said teeth.

3. The motor of claim 1 wherein said discrete facing comprises a hollow washer on each of said teeth, said washer being of a greater axial dimension than said teeth.

4. The motor of claim 1 wherein said discrete facing comprises a hollow washer on each of said teeth, said washer having an outer portion of the same axial dimension as said teeth and further having an inner portion of a greater axial dimension than said teeth.

5. The motor of claim 1 wherein said discrete facing is an alloy of cobalt, iron and vanadium.

6. The motor of claim 1 wherein said rotor means includes an elongated hollow tube of an electrically conductive material;

whereby said tube may be removed from an extrusion die or the like by the operation of said motor.

7. The motor of claim 6 wherein said rotor means further includes an axially stationary, elongated rotor core and said tube moves over said rotor core.

8. The motor of claim 7 wherein said rotor core may be a mandrel.

9. The motor of claim 1 wherein said rotor means includes an elongated solid wire or the like, said wire being of an electrically conductive material; 7

whereby said wire may be drawn from an extrusion die or the like by the operation of said motor.

10. The motor of claim 1 wherein said cylindrical stator includes a plurality of slots, and said coils have rectangular annular channels connected to said slots to define a fluid path;

and further including means for introducing air through said slots and fluid path and thus into said motor for cooling said motor. l 11. The motor of claim 1 wherein said rotor means includes a rotor core of magnetically permeable material, and whereby upon energization of said coils, the increased rotor forces are generated without magnetic saturation of the stator member, the facing or the rotor core.

12. The motor of claim 11 wherein said rotor core includes a material having higher magnetic permeability and saturation levels than those of iron.

13. The motor of claim 11 wherein said rotor core has an interior facing of a material having a higher magnetic permeability and saturation level than those of iron. 

1. A converging flux, concentric linear induction motor especially adapted for moving rotor means, over long distances, said rotor means having a generally circular cross-section and a length greatly exceeding its diameter, said motor comprising: a hollow, cylindrical stator member made of a material of high magnetic permeability and positioned to surround said rotor means concentrically; said stator member including a plurality of annular teeth having teeth faces, said teeth being longitudinally spaced apart to define annular slots therebetween; a plurality of energizable coils positioned in said slots and concentrically surrounding said rotor means, and a discrete facing on said teeth faces, said discrete facing being of a material having a higher magnetic permeability and saturation level than said stator member, said discrete facing being of a radial thickness sufficient to prevent magnetic saturation of both said discrete facing and said stator member; whereby upon energization of said coils, said small diameter rotor means is moved axially by the generation of increased rotor forces without magnetic saturation of the stator member or said discrete facing or rotor means.
 2. The motor of claim 1 wherein said discrete facing comprises a hollow washer on each of said teeth, said washer being of the same axial dimension as said teeth.
 3. The motor of claim 1 wherein said discrete facing comprises a hollow washer on each of said teeth, said washer being of a greater axial dimension than said teeth.
 4. The motor of claim 1 wherein said discrete facing comprises a hollow washer on each of said teeth, said washer having an outer portion of the same axial dimension as said teeth and further having an inner portion of a greater axial dimension than said teeth.
 5. The motor of claim 1 wherein said discrete facing is an alloy of cobalt, iron and vanadium.
 6. The motor of claim 1 wherein said rotor means includes an elongated hollow tube of an electrically conductive material; whereby said tube may be removed from an extrusion die or the like by the operation of said motor.
 7. The motor of claim 6 wherein said rotor means further includes an axially stationary, elongated rotor core and said tube moves over said rotor core.
 8. The motor of claim 7 wherein said rotor core may be a mandrel.
 9. The motor of claim 1 wherein said rotor means includes an elongated solid wire or the like, said wire being of an electrically conductive material; whereby said wire may be drawn from an extrusion die or the like by the operation of said motor.
 10. The motor of claim 1 wherein said cylindrical stator includes a plurality of slots, and said coils have rectangular annular channels connected to said slots to define a fluid path; and further including means for introducing air through said slots and fluid path and thus into saiD motor for cooling said motor.
 11. The motor of claim 1 wherein said rotor means includes a rotor core of magnetically permeable material, and whereby upon energization of said coils, the increased rotor forces are generated without magnetic saturation of the stator member, the facing or the rotor core.
 12. The motor of claim 11 wherein said rotor core includes a material having higher magnetic permeability and saturation levels than those of iron.
 13. The motor of claim 11 wherein said rotor core has an interior facing of a material having a higher magnetic permeability and saturation level than those of iron. 